A liquid crystal display (LCD) has advantages of thin shape, light weight and low consumption of electric power, compared with a cathode ray tube (CRT). Most of the commercially available liquid crystal displays usually use a twisted nematic liquid crystal. A liquid crystal display mode is classified into a birefringent mode and anoptical rotatory mode.
In a liquid crystal display of a birefringent mode, alignment of liquid crystal molecules is twisted over 90.degree.. The transmittance of the supper twisted nematic (STN) liquid crystal display is changed abruptly over a threshold voltage when applying voltage to the cell. Accordingly, the liquid crystal display of the birefringent mode can display a large image by a time-sharing addressing method, even though an electrode consists of a simple matrix without an active matrix (such as a thin layer transistor or diode). However, the liquid crystal display using the supper twisted liquid crystal molecule has a slow response speed (several hundreds milliseconds). Further, it is difficult for the simple matrix to display a gray scale image.
A liquid crystal display having an active matrix (e.g., TFT-LCD, MIM-LCD) uses a liquid crystal molecule twisted at 90.degree. of an optical rotatory mode. The twisted nematic liquid crystal display (TN-LCD) has a fast response speed (several ten milliseconds). Further, the TN-LCD can display an image of high contrast. Therefore, the TN-LCD is predominant over commercially available liquid crystal displays.
Color and contrast in an image displayed in a conventional liquid crystal display depend on the viewing angle. A liquid crystal display is inferior to CRT in the viewing angle dependence.
Japanese Patent Provisional Publication No. 6(1994)-214116, and U.S, Pat. Nos. 5,583,679, 5,646,703 disclose an optical compensatory sheet using discotic compounds. The optical compensatory sheet has a function of improving the viewing angle of the liquid crystal display.
The viewing angle of the liquid crystal display has been improved by using the optical compensatory sheet. However, the improved viewing angle is still inferior to that of CRT.